Patients suffering from cardiac disorders are subjected to e.g. scans by X-ray computed tomography scanners, provided this is necessary from a medical point of view and sensible for examining the heart, wherein a scan is understood to mean the recording of a multiplicity of 2D X-ray projections, from different projection directions, of the heart, usually whilst the heart or the patient is advanced relative to the X-ray recording system of the X-ray computed tomography scanner. The aim of the examination is the generation of high-quality and meaningful images of the heart, which often form the basis for a diagnosis.
Since the heart is a moving organ, every effort is made in the reconstruction of slice images and 3D images of the heart (which are created on the basis of the recorded 2D X-ray projections) that only those 2D X-ray projections recorded during the cardiac phase of the cardiac cycle of the patient in which the heart, where possible, was not going through any motion are used, in particular to avoid movement artifacts in the reconstructed slice images and 3D images of the heart. Here it is conventional for an electrocardiogram (EKG) of the heart of the patient to be recorded for establishing the cardiac cycle of the heart of the patient.
In order to increase the quality of generated images of the heart of a patient, it is desirable to lower the heart rate or the cardiac frequency of the heart of a patient when recording the 2D projections, as a result of which it is possible to lengthen the phase during which the heart and the blood vessels of the heart exhibit practically no motion. By way of example, the heart rate can be lowered by administering beta blockers; however, like any other medicament, these have side effects that should be avoided where possible. A further disadvantage of beta blockers is that their effect only sets in approximately 30 minutes after being taken, and so, undesirably, there can be waiting periods before the recording of the 2D projections is started.